1. Field of the Invention
This invention concerns punch presses and more particularly workpiece handling for punch presses.
2. Description of the State of the Art
Punch presses are conventionally configured with a C-shaped frame with the press ram located at the forward end of the upper C-frame member. Sheet material workpieces are movable within the throat opening in order to position the workpiece at the proper locations whereat punching is to be conducted.
Punch presses are typically automated, having a carriage with two or more gripper mechanisms gripping one edge of the sheet workpiece and traversing the same under a program control along orthogonal directions in a horizontal plane to various positions, bringing various locations on the workpiece to the punching station beneath the press ram. In many presses, the carriage-gripper assembly is located outside the throat opening holding the workpiece which extends back into the opening, other presses use so-called "rear address" carriages, in which the gripper-carriage assembly is disposed within the throat opening and the workpiece extends outwardly. In the rear address type of press, larger sheet sizes can be accommodated since the free end of a workpiece can project far out of the press throat area. However, the workpiece areas positionable at the punching station are limited since the carriage-gripper assembly outward travel is limited by the press throat depth.
Accordingly, it has heretofore been the practice to manually rotate the workpiece to reposition the far edge within the press throat opening, and a second phase of programmed punching then conducted in order to complete the punching on the rest of the workpiece. The need for manual intervention in the process slows the production rate and increases the production costs due to the extra labor required.
Punch presses are often equipped with tool holding upper and lower turrets to enable the various different punch-die tool sets to be selectively driven to the punching station.
Such tool sets have included indexing type drives which have the capability of rotating the tool in the station so as to allow orientations of the punching tool to be set.
It has heretofore been proposed that an indexing station be utilized to accomplish powered rotation of a workpiece to eliminate the need for manual handling. In this arrangement, the force of the press ram is used to press a worksheet engaging pad into frictional engagement with the workpiece and a rotary drive for the indexing station activated to accomplish rotation of the workpiece.
This approach has several disadvantages, however.
Firstly, the use of the indexing station dedicated to workpiece rotation for punch tooling is precluded, reducing the tooling selection available inasmuch as the particular indexing station so utilized obviously cannot also be used to accommodate tooling.
Secondly, this approach requires that hydraulic ram actuation be used, since the ram actuator must be capable of advancing the ram through a partial stroke and applying a predetermined pressure to the workpiece. Thus, conventional presses using mechanical ram drives cannot be adapted to the concept.
Finally, the accuracy of angular positioning of the workpiece achievable with such indexing drives is not great, thus making reliable processing difficult to achieve.
Accordingly, it is an object of the present invention to provide automated workpiece rotation in a punch press which is adapted to punch presses having mechanical, hydraulic, or other actuation means for the ram.
It is another object of the present invention to provide an automatic workpiece rotation which does not reduce the tooling capacity of the rotary turrets.
It is still another object of the present invention to provide an automated sheet rotation mechanism for rotary turret punch presses in which a high degree of positioning accuracy of the workpiece is easily achievable.